Amyloidosis is a diverse group of disease processes characterized by extracellular tissue deposits, in one or many organs, of protein materials which are generically termed amyloid. Amyloid may be distinguished grossly by a starch-like staining reaction with iodine (thus the term amyloid), microscopically by its extracellular distribution and tinctorial and optical properties when stained with Congo red, and by its protein fibril structure as shown by electron microscopy and x-ray crystallography (see Table 1). Exemplary amyloidosis diseases are Alzheimer's Disease (“AD”), Down's Syndrome, Type 2 diabetes mellitus, and mild cognitive impairment (MCI).
AD is a neurodegenerative illness characterized by memory loss and other cognitive deficits. McKhann et al., Neurology 34: 939 (1984). It is the most common cause of dementia in the United States. AD can strike persons as young as 40-50 years of age, yet, because the presence of the disease is difficult to determine without dangerous brain biopsy, the time of onset is unknown. The prevalence of AD increases with age, with estimates of the affected population reaching as high as 40-50% by ages 85-90. Evans et al., JAMA 262: 2551 (1989); Katzman, Neurology 43: 13 (1993).
Neuropathologically, AD is characterized by the presence of neuritic plaques (NP), neurofibrillary tangles (NFT), and neuronal loss, along with a variety of other findings. Mann, Mech. Ageing Dev. 31: 213 (1985). Post-mortem slices of brain tissue of victims of AD exhibit the presence of amyloid in the form of proteinaceous extracellular cores of the neuritic plaques that are characteristic of AD. The amyloid cores of these neuritic plaques are composed of a protein called the β-amyloid (Aβ) that is arranged in a predominately beta-pleated sheet configuration.
AD is believed to afflict some 4 million Americans and perhaps 20-30 million people worldwide. AD is recognized as a major public health problem in developed nations. Several therapeutic targets have emerged from the ongoing elucidation of the molecular basis of AD. For example, four cholinesterase inhibitors have been approved for the symptomatic treatment of patients with AD—tacrine (Cognex, Warner-Lambert, Morris Plains, N.J.); donepezil (Aricept, Eisai, Inc., Teaneck, N.J., and Pfizer, Inc., New York, N.Y.); rivagstigmine (Exelon, Novartis, Basel, Switzerland); and galantamine (Reminyl, Janssen, Titusville, N.J.). Potential new AD therapies that are currently being developed involve immunotherapy, secretase inhibitors or anti-inflammatory drugs. However, to date, there are no available drugs proven to modify the course of cognitive decline.
A major hurdle to developing anti-amyloid therapies is exemplified by the following quote from (Hock, C. et al., 2003, Neuron, 38:547-554), directed to use of immunotherapy as an anti-amyloid therapy: “[w]e do not know whether brain Aβ-amyloid load was reduced in our study patients; in vivo imaging techniques will be required to answer this question.” The ability to quantify amyloid load before treatment and then follow the effects of treatment is critical to the efficient development of this class of drugs. The present invention employs amyloid imaging as a surrogate marker of efficacy for anti-amyloid therapies.